Polymorphisms in drug-metabolizing enzymes and steady-state exemestane concentration in postmenopausal patients with breast cancer.

Discovery of clinical and genetic predictors of exemestane pharmacokinetics was attempted in 246 postmenopausal patients with breast cancer enrolled on a prospective clinical study. A sample was collected 2 h after exemestane dosing at a 1- or 3-month study visit to measure drug concentration. The primary hypothesis was that patients carrying the low-activity CYP3A4*22 (rs35599367) single-nucleotide polymorphism (SNP) would have greater exemestane concentration. Additional SNPs in genes relevant to exemestane metabolism (CYP1A1/2, CYP1B1, CYP3A4, CYP4A11, AKR1C3/4, AKR7A2) were screened in secondary analyses and adjusted for clinical covariates. CYP3A4*22 was associated with a 54% greater exemestane concentration (P<0.01). Concentration was greater in patients who reported White race, had elevated aminotransferases, renal insufficiency, lower body mass index and had not received chemotherapy (all P<0.05), and CYP3A4*22 maintained significance after adjustment for covariates (P<0.01). These genetic and clinical predictors of exemestane concentration may be useful for treatment individualization in patients with breast cancer.

Efavirenz-mediated induction of omeprazole metabolism is CYP2C19 genotype dependent.

Efavirenz increases CYP2C19- and CYP3A-mediated omeprazole metabolism. We hypothesized that CYP2C19 and CYP2B6 genetic polymorphisms influence the extent of induction of omeprazole metabolism by efavirenz. Healthy subjects (n=57) were administered a single 20 mg oral dose of omeprazole on two occasions: with a single 600 mg efavirenz dose; and after a 17-day treatment with efavirenz (600 mg per day). DNA was genotyped for CYP2C19*2, *3 and *17 alleles and CYP2B6*6, *4 and *9 alleles using Taqman assays. Omeprazole, its enantiomers and metabolites were measured by liquid chromatography/tandem mass spectrometry. Our results showed that efavirenz increased omeprazole clearances in all CYP2C19 genotypes in non-stereoselective manner, but the magnitude of induction was genotype dependent. Metabolic ratios of 5-hydroxylation of omeprazole were reduced in extensive and intermediate metabolizers of CYP2C19 (P<0.05). No significant associations were observed between CYP2B6 genotypes and induction by efavirenz on omeprazole metabolism. Our data indicate how interplays between drug interactions and CYP2C19 genetic variations may influence systemic exposure of CYP2C19 substrates.

Aromatase inhibitor-induced modulation of breast density: clinical and genetic effects.

BACKGROUND: Change in breast density may predict outcome of women receiving adjuvant hormone therapy for breast cancer. We performed a prospective clinical trial to evaluate the impact of inherited variants in genes involved in oestrogen metabolism and signalling on change in mammographic percent density (MPD) with aromatase inhibitor (AI) therapy. METHODS: Postmenopausal women with breast cancer who were initiating adjuvant AI therapy were enrolled onto a multicentre, randomised clinical trial of exemestane vs letrozole, designed to identify associations between AI-induced change in MPD and single-nucleotide polymorphisms in candidate genes. Subjects underwent unilateral craniocaudal mammography before and following 24 months of treatment. RESULTS: Of the 503 enrolled subjects, 259 had both paired mammograms at baseline and following 24 months of treatment and evaluable DNA. We observed a statistically significant decrease in mean MPD from 17.1 to 15.1% (P<0.001), more pronounced in women with baseline MPD ≥20%. No AI-specific difference in change in MPD was identified. No significant associations between change in MPD and inherited genetic variants were observed. CONCLUSION: Subjects with higher baseline MPD had a greater average decrease in MPD with AI therapy. There does not appear to be a substantial effect of inherited variants in biologically selected candidate genes.

Genome-wide discovery of genetic variants affecting tamoxifen sensitivity and their clinical and functional validation.

BACKGROUND: Beyond estrogen receptor (ER), there are no validated predictors for tamoxifen (TAM) efficacy and toxicity. We utilized a genome-wide cell-based model to comprehensively evaluate genetic variants for their contribution to cellular sensitivity to TAM. DESIGN: Our discovery model incorporates multidimensional datasets, including genome-wide genotype, gene expression, and endoxifen-induced cellular growth inhibition in the International HapMap lymphoblastoid cell lines (LCLs). Genome-wide findings were further evaluated in NCI60 cancer cell lines. Gene knock-down experiments were performed in four breast cancer cell lines. Genetic variants identified in the cell-based model were examined in 245 Caucasian breast cancer patients who underwent TAM treatment. RESULTS: We identified seven novel single-nucleotide polymorphisms (SNPs) associated with endoxifen sensitivity through the expression of 10 genes using the genome-wide integrative analysis. All 10 genes identified in LCLs were associated with TAM sensitivity in NCI60 cancer cell lines, including USP7. USP7 knock-down resulted in increasing resistance to TAM in four breast cancer cell lines tested, which is consistent with the finding in LCLs and in the NCI60 cells. Furthermore, we identified SNPs that were associated with TAM-induced toxicities in breast cancer patients, after adjusting for other clinical factors. CONCLUSION: Our work demonstrates the utility of a cell-based model in genome-wide identification of pharmacogenomic markers.

Pharmacogenomics of selective serotonin reuptake inhibitor treatment for major depressive disorder: genome-wide associations and functional genomics.

A genome-wide association (GWA) study of treatment outcomes (response and remission) of selective serotonin reuptake inhibitors (SSRIs) was conducted using 529 subjects with major depressive disorder. While no SNP associations reached the genome-wide level of significance, 14 SNPs of interest were identified for functional analysis. The rs11144870 SNP in the riboflavin kinase (RFK) gene on chromosome 9 was associated with 8-week treatment response (odds ratio (OR)=0.42, P=1.04 × 10⁻6). The rs915120 SNP in the G protein-coupled receptor kinase 5 (GRK5) gene on chromosome 10 was associated with 8-week remission (OR=0.50, P=1.15 × 10⁻5). Both SNPs were shown to influence transcription by a reporter gene assay and to alter nuclear protein binding using an electrophoretic mobility shift assay. This report represents an example of joining functional genomics with traditional GWA study results derived from a GWA analysis of SSRI treatment outcomes. The goal of this analytical strategy is to provide insights into the potential relevance of biologically plausible observed associations.

Efavirenz directly modulates the oestrogen receptor and induces breast cancer cell growth.

OBJECTIVES: Efavirenz-based HIV therapy is associated with breast hypertrophy and gynaecomastia. Here, we tested the hypothesis that efavirenz induces gynaecomastia through direct binding and modulation of the oestrogen receptor (ER). METHODS: To determine the effect of efavirenz on growth, the oestrogen-dependent, ER-positive breast cancer cell lines MCF-7, T47D and ZR-75-1 were treated with efavirenz under oestrogen-free conditions in the presence or absence of the anti-oestrogen ICI 182,780. Cells treated with 17ß-oestradiol in the absence or presence of ICI 182,780 served as positive and negative controls, respectively. Cellular growth was assayed using the crystal violet staining method and an in vitro receptor binding assay was used to measure the ER binding affinity of efavirenz. RESULTS: Efavirenz induced growth in MCF-7 cells with an estimated effective concentration for half-maximal growth (EC(50)) of 15.7 µM. This growth was reversed by ICI 182,780. Further, efavirenz binds directly to the ER [inhibitory concentration for half maximal binding (IC(50)) of ∼52 µM] at a roughly 1000-fold higher concentration than observed with 17ß-oestradiol. CONCLUSIONS: Our data suggest that efavirenz-induced gynaecomastia may be caused, at least in part, by drug-induced ER activation in breast tissues.

Cytochrome P450 2D6 activity predicts discontinuation of tamoxifen therapy in breast cancer patients.

The selective estrogen receptor modulator tamoxifen is routinely used for treatment and prevention of estrogen-receptor-positive breast cancer. Studies of tamoxifen adherence suggest that over half of patients discontinue treatment before the recommended 5 years. We hypothesized that polymorphisms in CYP2D6, the enzyme responsible for tamoxifen activation, predict for tamoxifen discontinuation. Tamoxifen-treated women (n=297) were genotyped for CYP2D6 variants and assigned a 'score' based on predicted allele activities from 0 (no activity) to 2 (high activity). Correlation between CYP2D6 score and discontinuation rates at 4 months was tested. We observed a strong nonlinear correlation between higher CYP2D6 score and increased rates of discontinuation (r(2)=0.935, P=0.018). These data suggest that presence of active CYP2D6 alleles may predict for higher likelihood of tamoxifen discontinuation. Therefore, patients who may be most likely to benefit from tamoxifen may paradoxically be most likely to discontinue treatment prematurely.

Enhancing race-based prescribing precision with pharmacogenomics.

In the world of medicine and therapeutics, race and ethnicity might reasonably be considered as biomarkers or predictors of drug effect. Recognizing that all biomarkers are imperfect, self-reported race can be viewed as a complex combination of genetic and nongenetic biomarkers that is used by prescribing physicians as a predictor of drug effect. The use of pharmacogenetic markers, such as haplotypes, patterns of candidate genes, and specific genotypes, may be used to enhance the precision of race-based prescribing and, when possible, should be combined with nongenetic predictors of responses to optimize the individualization of therapy.

The star-allele nomenclature: retooling for translational genomics.

The star-allele nomenclature is the result of efforts to standardize genetic polymorphism annotation for the cytochrome P450 genes. As clinical pharmacogenetic testing becomes widespread, it is important that this system effectively communicate a patient's genotype and predicted clinical phenotype. As genomics research expands, it is equally important that the system remain a valuable tool for the wider community of genetic researchers to exploit our ever-improving ability to catalog variability in the human genome.

Implementation of a pharmacogenomics consult service to support the INGENIOUS trial.

Hospital systems increasingly utilize pharmacogenomic testing to inform clinical prescribing. Successful implementation efforts have been modeled at many academic centers. In contrast, this report provides insights into the formation of a pharmacogenomics consultation service at a safety-net hospital, which predominantly serves low-income, uninsured, and vulnerable populations. The report describes the INdiana GENomics Implementation: an Opportunity for the UnderServed (INGENIOUS) trial and addresses concerns of adjudication, credentialing, and funding.

Identification and Mechanistic Investigation of Drug-Drug Interactions Associated With Myopathy: A Translational Approach.

Myopathy is a group of muscle diseases that can be induced or exacerbated by drug-drug interactions (DDIs). We sought to identify clinically important myopathic DDIs and elucidate their underlying mechanisms. Five DDIs were found to increase the risk of myopathy based on analysis of observational data from the Indiana Network of Patient Care. Loratadine interacted with simvastatin (relative risk 95% confidence interval [CI] = [1.39, 2.06]), alprazolam (1.50, 2.31), ropinirole (2.06, 5.00), and omeprazole (1.15, 1.38). Promethazine interacted with tegaserod (1.94, 4.64). In vitro investigation showed that these DDIs were unlikely to result from inhibition of drug metabolism by CYP450 enzymes or from inhibition of hepatic uptake via the membrane transporter OATP1B1/1B3. However, we did observe in vitro synergistic myotoxicity of simvastatin and desloratadine, suggesting a role in loratadine-simvastatin interaction. This interaction was epidemiologically confirmed (odds ratio 95% CI = [2.02, 3.65]) using the data from the US Food and Drug Administration Adverse Event Reporting System.

Age-Related Changes in MicroRNA Expression and Pharmacogenes in Human Liver.

Developmental changes in the liver can significantly impact drug disposition. Due to the emergence of microRNAs (miRNAs) as important regulators of drug disposition gene expression, we studied age-dependent changes in miRNA expression. Expression of 533 miRNAs was measured in 90 human liver tissues (fetal, pediatric [1-17 years], and adult [28-80 years]; n = 30 each). In all, 114 miRNAs were upregulated and 72 were downregulated from fetal to pediatric, and 2 and 3, respectively, from pediatric to adult. Among the developmentally changing miRNAs, 99 miRNA-mRNA interactions were predicted or experimentally validated (e.g., hsa-miR-125b-5p-CYP1A1; hsa-miR-34a-5p-HNF4A). In human liver samples (n = 10 each), analyzed by RNA-sequencing, significant negative correlations were observed between the expression of >1,000 miRNAs and mRNAs of drug disposition and regulatory genes. Our data suggest a mechanism for the marked changes in hepatic gene expression between the fetal and pediatric developmental periods, and support a role for these age-dependent miRNAs in regulating drug disposition.

Effect of clarithromycin on the pharmacokinetics and pharmacodynamics of pimozide in healthy poor and extensive metabolizers of cytochrome P450 2D6 (CYP2D6).

BACKGROUND: The use of pimozide is associated with prolongation of the QT interval and fatal ventricular arrhythmia. We recently reported 2 fatal cases in patients taking pimozide and clarithromycin and we have shown that clarithromycin inhibits CYP3A-mediated metabolism of pimozide in vitro. In this study, we examined the effect of clarithromycin on pimozide pharmacokinetics and QT interval changes in a total of 12 healthy subjects (7 men and 5 women), documented as extensive metabolizers or poor metabolizers of CYP2D6. METHODS: In a randomized, double-blind placebo-controlled crossover design, subjects were given a single 6-mg oral dose of pimozide after 5 days of treatment with clarithromycin (500 mg twice a day) or a placebo pill. Blood samples were obtained before and for 96 hours after pimozide administration, and plasma pimozide and clarithromycin concentrations were measured by HPLC. Electrocardiograms for the analysis of the QTc intervals were recorded immediately before each blood sample. RESULTS: Pimozide significantly lengthened QTc interval in the first 20 hours in both the placebo-treated groups (delta QTcmax = 13.3 +/- 5.3 ms; P = .003) and clarithromycin-treated groups (delta QTcmax = 15.7 +/- 9.5 ms; P = .005) compared with baseline values. This is consistent with an effect of the parent drug. Clarithromycin caused a significant increase in the peak plasma concentration (P = .015), terminal elimination half-life (P = .003), and area under the plasma concentration-time curve (P = .024) and a decrease in the clearance (P = .029) of pimozide. Mean QTcmax observed within 20 hours of pimozide administration was significantly greater in the clarithromycin-treated group (23.8 +/- 12.2 ms; P = .0397) than in the placebo-treated group (16.8 +/- 6 ms). There was no significant effect of CYP2D6 or gender on the pharmacokinetics or pharmacodynamics of pimozide. CONCLUSIONS: A single 6-mg oral dose of pimozide resulted in measurable QT interval changes. Clarithromycin inhibited CYP3A-mediated pimozide metabolism and the resulting elevation in plasma concentrations may increase the risk of pimozide cardiotoxicity.

Selection of drugs to treat gastro-oesophageal reflux disease: the role of drug interactions.

Gastro-oesophageal reflux disease is probably the most common acid-peptic disease in Western countries, and the successful treatment of mild to moderate disease with pharmacotherapy has become commonplace. A large number of effective drugs are now available, and so the decision-making process for physicians increasingly relies on considerations other than pure efficacy. Cost, adverse effects and drug interactions have therefore become important, particularly in the most vulnerable patients - children, the elderly and patients who are ill and are taking medications that may influence the efficacy of antireflux therapy. Important drug interactions with antacids include the prevention of the absorption of antibacterials such as tetracycline, azithromycin and quinolones. H2 antagonists, proton pump inhibitors and prokinetic agents undergo metabolism by the cytochrome P450 (CYP) system present in the liver and gastrointestinal tract. Cimetidine is an inhibitor of CYP3A and it may cause significant interactions with drugs of narrow therapeutic range and low bioavailability that are metabolised by these enzymes. The gastroparietal proton pump inhibitors lansoprazole, omeprazole and pantoprazole are all primarily metabolised by a genetically polymorphic enzyme, CYP2C19, that is absent from approximately 3% of Caucasians and 20% of Asians. These drugs may also interact with CYP3A, but to a lesser extent. Interactions with prokinetic agents carry the greatest potential for harm. Metoclopramide is a dopamine antagonist that may cause extrapyramidal effects when administered alone at high concentrations, or when coadministered with antipsychotic agents such as haloperidol or phenothiazines. Cisapride is clearly able to prolong the electrocardiographic QT interval and cause lethal ventricular arrhythmias when its metabolism is slowed by interaction with inhibitors of CYP3A, such as erythromycin, ketoconazole or itraconazole.

Pharmacodynamic interactions between isoniazid and theophylline in mice and rats, and the influence of pyridoxine.

Convulsions induced by acute administration of isoniazid (1), theophylline (2) as well as combinations of 1 and 2 were evaluated in male albino mice and male Wistar rats. The effect of pyridoxine (3) on these seizures was tested. Serum and brain levels of 1 after coadministration with 2 and caffeine (4) were assessed. The relevance of the observed pharmacokinetic phenomena in serum is questionable for the CNS processes because animals convulsed late (starting 90 min) and no significant changes of brain levels of 1 were observed. In conclusion, interactions of 1 and 2 may not occur through common mechanisms and exist only if the dose of 1 is toxic suggesting toxicological rather than therapeutic relevance.

Prescription writing in Gondar outpatient teaching hospital, Ethiopia.

A total of 19,119 prescriptions consecutively written between January-July 1992 were collected from Gondar outpatient hospital selling pharmacy and reviewed to determine physician's adherence to the basic principles of prescription order writing. In 36.6%, 16.8% and 12.4% of the prescriptions, respectively, age, sex and chart numbers of patients were not recorded. Twelve percent, 7%, 6.4%, 5.8% and 1.6% of the prescriptions did not indicate routes of drug administration, directions for drug use, frequency of drug administration, drug dose and duration of treatment, respectively. No prescription order had special advice or warnings to the patient and in 10.8% of the cases date was omitted. Out of the dispensed drugs, 82.9% were written in generic names and over 70% were included in the Essential Drug List of Ethiopia. The five most commonly dispensed individual drugs were ampicillin (10.4%), paracetamol (9.5%), TB 450 + isoniazid (7.4%), penicillin G (6.8%) and aspirin (5.8%). As therapeutic classes, antiinfectives were most common (47.8%) of which antibacterials constituted 38.1%, followed by analgesic-antipyretics (17.5%). Most drugs were prescribed by young medical interns and dispensed by less qualified personnel. Our preliminary survey indicates that essential components of a prescription order were omitted to a great extent and suggested to modify the existing undergraduate pharmacotherapeutic teaching in order to promote rational use and prescribing before bad habits get a chance to develop. The type of drugs dispensed at the selling pharmacy could not be beneficial to the patient without competent professional patient counselling, delivery of correct information as well as appropriate prescription monitoring.

Prescribing pattern of antibacterial drugs in a teaching hospital in Gondar, Ethiopia.

The prescribing pattern of antibacterial agents was analyzed by reviewing case notes of 407 patients discharged between October and November 1992 from a teaching hospital in Gondar, North-West Ethiopia. Seventy percent had received one or more antibacterials. Most exposure was in surgical ward (84%) followed by paediatric (82%), orthopaedic (78%), medical (72%), gynaecologic (58%) and obstetric (20%) wards. The antibacterials most frequently prescribed were penicillin G (25%), chloramphenical (24%), and ampicillin (20%). The total list numbered 13 and included no cephalosporines or quinoline derivatives. The preliminary survey indicated an inappropriate use of antibacterials and suggested the need to develop a policy on hospital antibacterial use.

Effects of isoniazid on hepatic drug oxidation and N-acetylation capacities in rats.

In vitro and in vivo activity of hepatic monooxygenase as well as in vivo N-acetylation capacity were assessed in male Wistar rats after oral pretreatment with 10 and 50 mg/kg isoniazid for 7 d. Both doses of isoniazid showed no statistical difference in protein contents, total cytochrome P-450 and the activities of aminopyrine N-demethylase as well as ethoxyresorufin-O-deethylase in the 9000 x g liver homogenate suspension compared to the saline pretreated group. Body and relative liver weights remained also unchanged. In vivo isoniazid pretreatment with either dose hardly changed the kinetic profiles and parameters of phenazone and sulfadimidine (free + total). The results suggest that drug metabolizing pathways that can be evaluated by the metabolism of the model substances employed here may not be modified by prolonged isoniazid treatment.

Assessment of rational drug use and prescribing in primary health care facilities in north west Ethiopia.

A study on rational drug use was undertaken in nine health centres (HCs) and nine health stations (HSs) in Ethiopia. Prescribing, patient care and facility specific factors were measured using drug use indicators. Prescribing patterns of drugs were also assessed. With only few exceptions, the drug use indicators in HCs and HSs and between retrospective and prospective studies were similar despite differences in manpower and facilities. The average consultation time (in minutes) in HSs and HCs was 5.1 +/- 0.8 and 5.8 +/- 1.06, respectively. The dispensing time (in minutes) was 1.5 +/- 0.7 in HSs and 1.9 +/- 0.6 in HCs. Both patient care indicators seem to be adequate to influence patient satisfaction to the overall health service and patient knowledge of important dosage instructions. Most drugs (more than 89% in HCs and 71% in HSs) were actually dispensed from the health facilities and labelling was satisfactory. Prescribing by generic names (average: 75% in HCs and 83% in HSs) was encouraging. While the availability of key drugs was ensured, essential documents were missing in most facilities or they were unpopular for use, and those available required revision and updating. Polypharmacy in which the number of drugs/encounter was < 2.5 was minimal, but that a large proportion of the prescriptions contained two or more drugs could result in adverse drug-drug interactions. The most frequently prescribed drugs were anti-infectives and analgesics accounting for over 76% in HCs and 82% in HSs and in most cases they are probably prescribed with little justification. The exposure of patients to antibiotics (average: 60% in HCs and 65% in HSs) was unacceptably high to justify epidemiological trends. The high exposure of patients to injections, especially in the HSs (over 37%), should be seen from the health and economic points of view. The results revealed priority areas for intervention. They also provide standard references to compare drug use situations and their change over time in different settings, area and time in Ethiopia.

PIP: In a study on rational drug use in 9 health centers (HC) and 9 health stations (HS) in Ethiopia, prescribing, patient care, and facility-specific factors were observed and measured through drug use indicators during February-June 1995. With only few exceptions, the drug use indicators in HCs and HSs were similar despite differences in manpower and facilities. The average consultation times in minutes in HSs and HCs were 5.1 and 5.8, respectively, while the dispensing times were 1.5 and 1.9 minutes, respectively. More than 89% of drugs in HCs and 71% in HSs were dispensed from the health facilities, and labeling was satisfactory. On average, generic brands were prescribed 75% of the time in HCs and 83% of the time in HSs. Key drugs were available, but important documents were missing in most facilities or were unpopular for use. When documents were available, they needed to be revised and updated. The level of polypharmacy was low. The most often prescribed drugs were anti-infectives and analgesics, accounting for more than 76% in HCs and 82% in HSs, and probably often prescribed with little justification. 60% of patients in HCs and 65% in HSs were exposed to antibiotics, levels too high for the prevailing disease conditions. More than 37% of HS patients received injections.

Population pharmacogenetic-based pharmacokinetic modeling of efavirenz, 7-hydroxy- and 8-hydroxyefavirenz.

The purpose of this study was to determine the demographic and pharmacogenetic covariates that influence the disposition of efavirenz (EFV) and its major metabolites. A population pharmacokinetic (PK) model was developed from a randomized, cross-over, drug-interaction study in healthy male Korean subjects (n = 17). Plasma concentrations of EFV and its hydroxy-metabolites (0-120 hours) were measured by LC/MS/MS. Genomic DNA was genotyped for variants in the cytochrome P450 (CYP) 2A6, 2B6, 3A5, and MDR1 genes. A PK model was built in a stepwise procedure using nonlinear mixed effect modeling in NONMEM 7. The covariate model was built using the generalized additive modeling and forward selection-backward elimination. Model-based simulations were performed to predict EFV steady-state concentrations following 200, 400, and 600 mg daily oral dose among different CYP2B6 genotypes. The final model included only CYP2B6 genotype as a covariate that predicts EFV clearance through the formation of 8-OH EFV that represented 65% to 80% of EFV clearance. The total clearance of EFV in CYP2B6*6/*6 genotype was ∼30% lower than CYP2B6*1/*1 or CYP2B6*1/*6 alleles (P < .001). Clopidogrel reduced both formation and elimination clearances of 8-OH EFV by 22% and 19%, respectively (P = .033 and .041). Other demographics and genotype of accessory CYP pathways did not predict EFV or metabolites PK. CYP2B6 genotype was the only significant predictor of EFV disposition. The developed model may serve as the foundation for further exploration of pharmacogenetic-based dosing of EFV.